Manganese dioxide (Mno.sub.2) in an important raw material which is used extensively in the production of dry batteries due to the fact that when used in making the battery cells it can greatly effect the efficiency of the cell under certain discharging conditions as determined by the quantity of electric energy produced and the ability of the cell to supply electric current at all. The various types of manganese oxides which the battery manufacturers currently use in making batteries of the so-called Leclanche type, due to their oxidizing properties as depolarizers, are distinguishable according to their origin as follows:
(a) Natural manganese dioxides which are extracted from minerals by dressing wherein removal of some of the minor constituents results in an increase in the manganese dioxide percentage; PA1 (b) Natural inactive manganese oxides which have been subjected to chemical activation; PA1 (c) Manganese dioxides which have been produced electrolytically; and PA1 (d) Synthetic manganese oxides. PA1 (1) an increase in the recovery of the mineral; PA1 (2) production of a concentrate having an increased MnO.sub.2 percentage, i.e. of approximately 80% by weight or more, by treating ores which by prior art processes could not be profitably processed; at the same time reducing the CO.sub.2 content of the product to lower than 1%, PA1 (3) production of a product mineral which shows superior electro-chemical properties due to acid treatment of the ore to obtain a product having an increased MnO.sub.2 percentage; and PA1 (4) production of a product mineral which provides an improved stability of the heavy metal compounds in dry battery cells against the electrolyte solution (Stability Test), depending on the type of ore treated.
The natural manganese dioxides of (a) are characterized as being either "active" or "inactive" according to their suitability as depolarizers in the manufacture of dry cells. Natural manganese dioxides occur in various forms and types and are generally dressed up to 75-80% by weight of MnO.sub.2, based on the requirements of dry battery manufacturers, and the final product is introduced into commerce in powdered form having a grain size of less than 0.15 mm.
Upgrading of such powdered MnO.sub.2 is carried out by crushing, sizing and separation by gravity and based on the differences in bulk density. The concentrate almost always includes foreign matter, the percentage of which fluctuates between 20 and 30% by weight, due to the earth formations found adjacent to the deposits of the mineral. Such foreign matter includes compounds which are considered to be harmless (inert), such as silicates, or other compounds which are in fact detrimental (in terms of their influence of the discharging capacity of the dry cells which utilize the MnO.sub.2), such as carbonates or the soluble compounds of heavy metals (soluble in electrolyte solution).
In nature there are found active manganese dioxide ores which include exceptionally high percentages of carbonates, which carbonates are so finely distributed in the mass of the manganese dioxide that upgrading by mechanical methods is impossible, or else in such cases where mechanical methods are relatively successful, further dressing is nevertheless completely unprofitable because of the low mineral recovery.
It is thus an object of the present invention to provide a method for the production of a mineral concentrate which is high in MnO.sub.2 and which shows improved electrochemical properties by suitably treating in ore which is rich in carbonates of the above-discussed type or by suitably treating a pre-concentrate of such an ore.